A small number of serotypes are responsible for most invasive pneumococcal disease in children worldwide. Serotypes 1 and 5 were among the first pneumococcal serotypes to be identified, reflecting their great prominence as causes of disease in the early part of the 20th century. In the antibiotic era, these serotypes persist as important causes of disease in children in most countries even though they, unlike some other common serotypes, remain sensitive to antimicrobial agents. These types also exhibit a high level of virulence, cause disease clusters or outbreaks, infect all age groups, and cause severe disease. Future vaccine formulations that protect against these types are important for developed and developing countries alike.